A display panel device equipped with a touch panel for touch input is disclosed in a large number of documents. For example, JP 2002-040243A (Patent Document 1), JP 2002-055780A (Patent Document 2) and JP 2002-156920A (Patent Document 3) disclose a display panel device in which a touch panel for touch input is disposed on an upper side of a display panel board. All of the touch panels described in the Patent Documents 1 to 3 are a resistive type in which two transparent electrodes are disposed in a spaced-apart and opposed relation, wherein one of the transparent electrodes disposed on a viewing side of the display panel device is adapted to be pressed and brought into contact with the other transparent electrode, thereby allowing a tough input to be sensed. In the Patent Documents 1 to 3, there is an air gap between the two electrodes, which leads to a problem that reflected light in surfaces of the electrodes is transmitted to the viewing side of the display panel device, causing deterioration in display quality. In order to cope with this problem of internal reflection, the Patent Documents 1 to 3 teach arranging a circular polarization element on the viewing side with respect to the touch panel. Specifically, the Patent Documents 1 to 3 propose to arrange a linear polarization layer and a ¼λ retardation (phase difference) layer in this order from the viewing side of the display panel, and arrange the touch panel on a lower side of the ¼λ retardation layer. The Patent Document 1 discloses a configuration in which a touch panel is combined with a reflective liquid crystal display, and the Patent Document 2 mentions applicability to both a liquid crystal display and an organic EL display. Further, the Patent Document 3 offers an example of an organic EL display.
JP 2010-198103A (Patent Document 4) discloses a capacitive touch input device. A touch sensor described in the Patent Document 4 comprises two patterned electrically conductive layers each provided on a respective one of opposite sides of a substrate film formed as a single body. A touch sensor having a similar laminate configuration is described in FIG. 5 of JP 2009-076432A (Patent Document 5). The Patent Document 5 further describes, in FIG. 7 thereof, a double-electrode type touch sensor prepared by: forming a transparent electrode layer on one surface of a film substrate through an undercoat layer; bonding the other surface of the film substrate to a second film substrate through an adhesive layer; and forming a second transparent electrode layer on the second film substrate through a second undercoat layer. Details of patterning of a transparent electrode for use in a touch sensor are described in WO 2006/126604A.
JP 03-009323A (Patent Document 7) teaches selecting an appropriate material under recognition of a necessity to achieve optical isotropy without the occurrence of colored interference fringes, when a resin material is used in an electrode substrate for a liquid crystal display panel. JP 3542838B (Patent Document 8) and JP 3569557B (Patent Document 9) describe using an optically isotropic resin material as a material for an electrically conductive transparent sheet for a touch panel. In the Patent Documents 7 and 8, a recommended optically isotropic resin material includes a polycarbonate-based resin, a polyethersulfone-based resin, a polysulfone-based resin, and a polyarylate-based resin.